1. Field of Invention
The present invention relates to a solid state imaging device and a method for driving the same, more particularly relates to a technique for stabilizing loads applied upon circuits generating signals for transferring or discarding charges stored in opto-electro converting elements in a solid state imaging device. The present invention further relates to an imaging apparatus using the solid state imaging device.
2. Description of the Art
For example, Japanese Patent Publication (A) No. 2001-511628 discloses an imaging apparatus using a CMOS image sensor of a column unit reading type which simultaneously selects one read column and a plurality of shutter columns and transfers or discards charges stored in photodiodes (opto-electro converting elements) in the selected columns so as to realize a focal plane shutter.
In the imaging apparatus using this type of CMOS image sensor, when it is necessary to make a frame rate constant, a dummy period during which signals are not read from the actual effective pixels becomes necessary. To make the exposure times of the effective pixels constant, during the dummy period, columns including effective pixels cannot be selected as a pixel signal reading column (read columns) or shutter columns.
Further, when there is a plurality of shutter columns as well, columns including effective pixels cannot be selected as shutter columns in the dummy period during which it is not necessary operate the shutter in a camera device and block light.
Hitherto, no suitable measure has been taken for columns selected during the dummy period. The number of selected columns could change during operation as well. If the number of selected columns changes, the load applied upon the circuit for generating the signals for transferring or discarding charges stored in the photodiodes changes. Therefore, the reference potential level fluctuates or the charge transfer efficiency varies. This becomes a cause of an afterimage.